Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$128.57	12.540%	$144.6927	$144.69	$144.70	$144.70
Purchase #2	$19.75	10.651%	$21.8536	$21.85	$21.85	$21.90
Purchase #3	$44.85	4.329%	$46.7916	$46.79	$46.80	$46.80
Purchase #4	$231.87	10.638%	$256.5363	$256.54	$256.55	$256.50
Purchase #5	$139.99	5.727%	$148.0072	$148.01	$148.00	$148.00
Purchase #6	$129.56	10.259%	$142.8516	$142.85	$142.85	$142.90
Purchase #7	$52.97	11.729%	$59.1829	$59.18	$59.20	$59.20
7 purchase totals =	$747.56		$819.9159	$819.91	$819.95	$820.00